misc-redundant-expression: expression with calls to a non-pure function is considered as always-true

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Bugzilla Link	PR36505
Status	NEW
Importance	P enhancement
Reported by	Pavel Kryukov (pavel.kryukov@phystech.edu)
Reported on	2018-02-24 04:45:22 -0800
Last modified on	2021-11-21 10:16:54 -0800
Version	unspecified
Hardware	PC Windows NT
CC	alexfh@google.com, djasper@google.com, etienneb+llvm@google.com, eugene.zelenko@gmail.com, klimek@google.com, llvm-bugs@lists.llvm.org, xazax.hun@gmail.com
Fixed by commit(s)
Attachments	ldfile.c (282 bytes, text/x-csrc)
Blocks
Blocked by
See also

Created attachment 19951
Example of always-true false positive with calls to a non-pure function

Clang-Tidy produces a false positive warning about always-true expression (misc-
redundant-expression check) if expression contains consequent calls to a non-
pure function which have different return values:

$> clang-tidy -checks='*' ldfile.c -- -Wall
15 warnings generated.
./ldfile.c:11:32: warning: logical expression is always true [misc-redundant-
expression]
    if ((token = yylex()) != 1 || (token = yylex()) != 2) {
                               ^
Suppressed 14 warnings (14 in non-user code).

$> clang ldfile.c -Wall -Wextra && ./a.out
false

The code is taken from GNU Binutils (/ld/ldfile.c) source file.

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Attached ldfile.c (282 bytes, text/x-csrc): Example of always-true false positive with calls to a non-pure function

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Issue is reproducable in Clang-Tidy 6.0.0

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Still there in Clang-Tidy 7.0.0

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Reproduced with Clang-Tidy 9.0.1

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Same thing for Clang-Tidy 10.
Godbolt example: https://godbolt.org/z/w7PggB

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Reproduced with Clang-Tidy 11.0.0: https://godbolt.org/z/6nWMMa

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Reproduced with Clang-Tidy 13.0.0: https://godbolt.org/z/s5zcrzqhs

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Reproduced with Clang-Tidy 13.0.0: https://godbolt.org/z/s5zcrzqhs